[truetype] Keep variation store consistent.

`tt_var_load_item_variation_store` fills out a `GX_ItemVarStore`.  While it
may return an error, the item store must be left in a consistent state so
that any use or destruction of the item store can properly use or free the
data in it.  Before this change the counts from the font data were read
directly into the item store before the actual allocation of the arrays to
which they referred.  There exist many opportunities between the time the
counts are read and the arrays are allocated to return early due to invalid
data.  When this happened the item store claimed to have entires it actually
did not, leading to crashes later when it was used.

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=54449

* src/truetype/ttgxvar.c (tt_var_load_item_variation_store): Read the counts
into local variables and store them in the item store only after the related
arrays are actually created on the item store.

1 files changed, 54 insertions, 45 deletions

diff --git a/src/truetype/ttgxvar.c b/src/truetype/ttgxvar.c
index d2452f88c..7422fe008 100644
--- a/src/truetype/ttgxvar.c
+++ b/src/truetype/ttgxvar.c
@@ -502,13 +502,15 @@
     FT_Error   error;
     FT_UShort  format;
     FT_ULong   region_offset;
-    FT_UInt    i, j, k;
-    FT_UInt    wordDeltaCount;
-    FT_Bool    long_words;
 
-    GX_Blend        blend = face->blend;
-    GX_ItemVarData  varData;
+    FT_UInt    data_count;
+    FT_UShort  axis_count;
+    FT_UInt    region_count;
 
+    FT_UInt  i, j, k;
+    FT_Bool  long_words;
+
+    GX_Blend   blend           = face->blend;
     FT_ULong*  dataOffsetArray = NULL;
 
 
@@ -525,12 +527,12 @@
     }
 
     /* read top level fields */
-    if ( FT_READ_ULONG( region_offset )         ||
-         FT_READ_USHORT( itemStore->dataCount ) )
+    if ( FT_READ_ULONG( region_offset ) ||
+         FT_READ_USHORT( data_count )   )
       goto Exit;
 
     /* we need at least one entry in `itemStore->varData' */
-    if ( !itemStore->dataCount )
+    if ( !data_count )
     {
       FT_TRACE2(( "tt_var_load_item_variation_store: missing varData\n" ));
       error = FT_THROW( Invalid_Table );
@@ -539,10 +541,10 @@
 
     /* make temporary copy of item variation data offsets; */
     /* we will parse region list first, then come back     */
-    if ( FT_QNEW_ARRAY( dataOffsetArray, itemStore->dataCount ) )
+    if ( FT_QNEW_ARRAY( dataOffsetArray, data_count ) )
       goto Exit;
 
-    for ( i = 0; i < itemStore->dataCount; i++ )
+    for ( i = 0; i < data_count; i++ )
     {
       if ( FT_READ_ULONG( dataOffsetArray[i] ) )
         goto Exit;
@@ -552,11 +554,11 @@
     if ( FT_STREAM_SEEK( offset + region_offset ) )
       goto Exit;
 
-    if ( FT_READ_USHORT( itemStore->axisCount )   ||
-         FT_READ_USHORT( itemStore->regionCount ) )
+    if ( FT_READ_USHORT( axis_count )   ||
+         FT_READ_USHORT( region_count ) )
       goto Exit;
 
-    if ( itemStore->axisCount != (FT_Long)blend->mmvar->num_axis )
+    if ( axis_count != (FT_Long)blend->mmvar->num_axis )
     {
       FT_TRACE2(( "tt_var_load_item_variation_store:"
                   " number of axes in item variation store\n" ));
@@ -565,9 +567,10 @@
       error = FT_THROW( Invalid_Table );
       goto Exit;
     }
+    itemStore->axisCount = axis_count;
 
     /* new constraint in OpenType 1.8.4 */
-    if ( itemStore->regionCount >= 32768U )
+    if ( region_count >= 32768U )
     {
       FT_TRACE2(( "tt_var_load_item_variation_store:"
                   " too many variation region tables\n" ));
@@ -575,16 +578,16 @@
       goto Exit;
     }
 
-    if ( FT_NEW_ARRAY( itemStore->varRegionList, itemStore->regionCount ) )
+    if ( FT_NEW_ARRAY( itemStore->varRegionList, region_count ) )
       goto Exit;
+    itemStore->regionCount = region_count;
 
     for ( i = 0; i < itemStore->regionCount; i++ )
     {
       GX_AxisCoords  axisCoords;
 
 
-      if ( FT_NEW_ARRAY( itemStore->varRegionList[i].axisList,
-                         itemStore->axisCount ) )
+      if ( FT_NEW_ARRAY( itemStore->varRegionList[i].axisList, axis_count ) )
         goto Exit;
 
       axisCoords = itemStore->varRegionList[i].axisList;
@@ -608,47 +611,53 @@
     /* end of region list parse */
 
     /* use dataOffsetArray now to parse varData items */
-    if ( FT_NEW_ARRAY( itemStore->varData, itemStore->dataCount ) )
+    if ( FT_NEW_ARRAY( itemStore->varData, data_count ) )
       goto Exit;
+    itemStore->dataCount = data_count;
 
-    for ( i = 0; i < itemStore->dataCount; i++ )
+    for ( i = 0; i < data_count; i++ )
     {
-      varData = &itemStore->varData[i];
+      GX_ItemVarData  varData = &itemStore->varData[i];
+
+      FT_UInt  item_count;
+      FT_UInt  word_delta_count;
+      FT_UInt  region_idx_count;
+
 
       if ( FT_STREAM_SEEK( offset + dataOffsetArray[i] ) )
         goto Exit;
 
-      if ( FT_READ_USHORT( varData->itemCount )      ||
-           FT_READ_USHORT( wordDeltaCount )          ||
-           FT_READ_USHORT( varData->regionIdxCount ) )
+      if ( FT_READ_USHORT( item_count )       ||
+           FT_READ_USHORT( word_delta_count ) ||
+           FT_READ_USHORT( region_idx_count ) )
         goto Exit;
 
-      long_words      = !!( wordDeltaCount & 0x8000 );
-      wordDeltaCount &= 0x7FFF;
+      long_words        = !!( word_delta_count & 0x8000 );
+      word_delta_count &= 0x7FFF;
 
       /* check some data consistency */
-      if ( wordDeltaCount > varData->regionIdxCount )
+      if ( word_delta_count > region_idx_count )
       {
         FT_TRACE2(( "bad short count %d or region count %d\n",
-                    wordDeltaCount,
-                    varData->regionIdxCount ));
+                    word_delta_count,
+                    region_idx_count ));
         error = FT_THROW( Invalid_Table );
         goto Exit;
       }
 
-      if ( varData->regionIdxCount > itemStore->regionCount )
+      if ( region_idx_count > itemStore->regionCount )
       {
         FT_TRACE2(( "inconsistent regionCount %d in varData[%d]\n",
-                    varData->regionIdxCount,
+                    region_idx_count,
                     i ));
         error = FT_THROW( Invalid_Table );
         goto Exit;
       }
 
       /* parse region indices */
-      if ( FT_NEW_ARRAY( varData->regionIndices,
-                         varData->regionIdxCount ) )
+      if ( FT_NEW_ARRAY( varData->regionIndices, region_idx_count ) )
         goto Exit;
+      varData->regionIdxCount = region_idx_count;
 
       for ( j = 0; j < varData->regionIdxCount; j++ )
       {
@@ -664,33 +673,33 @@
         }
       }
 
-      /* Parse delta set.                                                */
-      /*                                                                 */
-      /* On input, deltas are (wordDeltaCount + regionIdxCount) bytes    */
-      /* each if `long_words` isn't set, and twice as much otherwise.    */
-      /*                                                                 */
-      /* On output, deltas are expanded to `regionIdxCount` shorts each. */
-      if ( FT_NEW_ARRAY( varData->deltaSet,
-                         varData->regionIdxCount * varData->itemCount ) )
+      /* Parse delta set.                                                  */
+      /*                                                                   */
+      /* On input, deltas are (word_delta_count + region_idx_count) bytes  */
+      /* each if `long_words` isn't set, and twice as much otherwise.      */
+      /*                                                                   */
+      /* On output, deltas are expanded to `region_idx_count` shorts each. */
+      if ( FT_NEW_ARRAY( varData->deltaSet, item_count * region_idx_count ) )
         goto Exit;
+      varData->itemCount = item_count;
 
-      for ( j = 0; j < varData->itemCount * varData->regionIdxCount; )
+      for ( j = 0; j < item_count * region_idx_count; )
       {
         if ( long_words )
         {
-          for ( k = 0; k < wordDeltaCount; k++, j++ )
+          for ( k = 0; k < word_delta_count; k++, j++ )
             if ( FT_READ_LONG( varData->deltaSet[j] ) )
               goto Exit;
-          for ( ; k < varData->regionIdxCount; k++, j++ )
+          for ( ; k < region_idx_count; k++, j++ )
             if ( FT_READ_SHORT( varData->deltaSet[j] ) )
               goto Exit;
         }
         else
         {
-          for ( k = 0; k < wordDeltaCount; k++, j++ )
+          for ( k = 0; k < word_delta_count; k++, j++ )
             if ( FT_READ_SHORT( varData->deltaSet[j] ) )
               goto Exit;
-          for ( ; k < varData->regionIdxCount; k++, j++ )
+          for ( ; k < region_idx_count; k++, j++ )
             if ( FT_READ_CHAR( varData->deltaSet[j] ) )
               goto Exit;
         }